The invention is based on a device for measuring a mass of a flowing medium, also known as a flow rate meter.
A device has already been proposed in German Patent Disclosure DE 44 07 209 A1 that has a substrate body, extending crosswise to the flow of the medium, that is introduced in plug-in fashion into an opening made in a boundary wall of the flow. The boundary wall is for instance a wall of an intake tube, through which an internal combustion engine aspirates air from the environment. The substrate body has an elongated shape, and on its free end region protruding into the flowing medium it has a measurement conduit, through which the medium flows. A temperature-dependent measuring element, embodied by so-called micromechanical engineering, is accommodated in the measurement conduit. Such measuring elements are known, for instance from German Patent Disclosure DE 195 24 634 A1 and have a sensor region, produced on a chip-like substrate by being etched out of a silicon wafer; with a plurality of resistance layers, this sensor region forms at least one temperature-dependent measuring resistor. The sensor region occupies only a small portion of the substrate and has an extremely slight thickness, so that the sensor region can detect changes in the flow speed, which means changes in the mass of the flowing medium, with a fast reaction time.
In engine operation, the opening and closing of the inlet valves of the engine causes a highly pulsating flow in the intake tube which is turbulent in character. The influence of the pulsations in the flow is damped by accommodating the measuring element in the measurement conduit.
From German Patent Disclosure DE 44 41 874 A1, it is known to provide a flow obstacle, which causes a defined flow separation operative in the measurement conduit, at the inlet opening of the measurement conduit. This flow obstacle may for instance be a trip edge or a trip wire. This provision reduces the turbulence in the flow conduit, which in turn is expressed in reduced measurement signal noise.
From German Patent Disclosure DE 43 40 882 A1, it is known, in a measurement conduit of a device for measuring the mass of a flowing medium, to provide an internal sleeve with a friction face. At the friction face, eddies are induced, which vary the flow resistance and thus lead to an intended measurement correction. Instead of the inner sleeve, laminations can also be provided as means for varying the flow.
The measuring device according to the invention has an advantage over the prior art that by suitable dimensioning of the protuberance, the measuring device can be adapted with especially fine sensitivity, and systematic measurement errors caused by the flow pulsation can be eliminated or at least reduced. While the pulsation error is already roughly minimized by suitably dimensioning the length, flow resistance, and conduit cross section of the measurement conduit, a very finely sensitive variation and hence minimization of the pulsation error is attainable by optimizing the disposition, shape, length, height and other parameters of the protuberance provided in the surroundings of the outlet opening of the deflection conduit.
Advantageous refinements of and improvements to the measuring device defined herein are possible with the provisions recited herein after.
The protuberance can be provided both in an upstream ambient region of the outlet opening of the deflection conduit in terms of the primary flow direction in the line and in a downstream ambient region thereof in terms of the primary flow direction in the line. If the protuberance is provided upstream of the outlet opening, the pulsation error is shifted in the direction of an underindication. Conversely, if the protuberance is provided downstream of the outlet opening in terms of the primary flow direction, the pulsation error is shifted in the direction of an overindication.
If the protuberance is provided in the upstream ambient region of the outlet opening in terms of the primary flow direction, then the outlet opening preferably has a separation edge, which is embodied either with a sharp edge or has a very short radius of curvature. The protuberance is advantageously disposed such that the protuberance protrudes past the outlet opening; that is, a plane touching the separation edge and extending perpendicular to the primary flow direction in the line intersects the outlet opening. The protuberance preferably has a substantially triangular cross-sectional contour, where one corner of the triangular cross-sectional contour forms the separation edge and a further corner of the triangular cross-sectional contour coincides with an upstream end of the outlet opening.
If the protuberance is disposed in the downstream ambient region of the outlet opening in terms of the primary flow direction, then it is advantageous for the protuberance to be rounded, at least in an end region oriented in the primary flow direction. The protuberance is preferably shaped in undulating fashion and curved steadily in such a way that in the region downstream in terms of the flow direction in the line the protuberance changes over without forming an edge into a plain in which the outer face having the outlet opening extends. The result in the region of the protuberance is a relatively slight turbulence in the flow, and the protuberance presents only relatively slight flow resistance to the primary flow in the line.